bogey21
TUG Member
It doesn't matter how long it takes to get there - the documented date of mailing is what counts.
I thought I said that OP wants "proof of mailing".
My concern with Registered Mail is that it sometimes takes forever to get to addressee which will at best slow down any refund due so yes, it can matter how long it takes to get there. A few years ago I liquidated a collection of old casino chips most of which I sent Registered Mail. Three to six weeks for delivery was not unusual. Why should OP unnecessarily extend the length of time it will take to know he is off the hook and to get his refund?
George